SHEET

OF

1

RESORT VILLAGECounty Of San Diego, California

OTAY RANCH

1

PREPARED BY:

DISCHARGE PIPING

LOW FLOW STORM DRAIN

OUTLET

TURF BOX RISER

ORIFICE

LEGEND COLOR

TRIBUTARY AREAS

DEVELOPED AREANOT TRIBUTARY TO WQ BASIN*

AREA DESCRIPTION

NATURAL AREATRIBUTARY TO WQ BASIN

NATURAL AREANOT TRIBUTARY TO WQ BASIN

*IMPERVIOUS DEVELOPED AREAS NOT DRAINING TO WATER QUALITY BASINS SHALL BE TREATED BY FILTERRA UNITS PRIOR TO DISCHARGING INTO RESERVOIR

LEGEND:WATER QUALITY BASIN

INLET INSERT WITH BIOGREEN MEDIA FILTER OREQUIVALENT AS PART OF TREATMENT TRAIN

FILTERRA UNIT

CULVERT LOCATION ALONG OTAY LAKES RD

RESERVOIR WATER SURFACE ELEVATION 490.7

DEVELOPED AREATRIBUTARY TO WQ BASIN

SITE DESIGN BMP's & LOW IMPACT DESIGN

- MINIMIZE IMPERVIOUS FOOTPRINT

- MINIMIZE EROSION FROM SLOPES

- MINIMIZE DISTURBANCE TO NATURAL DRAINAGES

- MINIMIZE SOIL COMPACTION

- DRAIN RUNOFF FROM IMPERVIOUS AREAS TO PERVIOUS AREAS

- CONSERVE NATURAL AREAS & DRAINAGES

TREATMENT CONTROL BMP's

- WATER QUALITY BASIN

- INLET INSERT WITH ADVANCED MEDIA FILTER

- VEGETATED SWALE

- FILTERRA UNIT

SOURCE CONTROL BMP's

- STORM DRAIN INLET STENCILING

- LANDSCAPE/OUTDOOR PESTICIDE USE

AREA (AC)

683

132

333

1343

THE CITY OF SAN DIEGO

M E M O R A N D U M

DATE: February 13, 2012 TO: Jeanette Temple, Development Project Manager, Development Services FROM: Jeffery Pasek, Watershed Manager, Long-Range Planning & Water Resources

Division SUBJECT: Otay Ranch Resort, Public Utilities’ review of report on salt and nutrient loading ____________________________________________________________________________ Dexter Wilson Engineering, consultants to Baldwin & Sons, prepared a memorandum that reports on their assessment of salt and nutrient loading to Lower Otay Reservoir from the Otay Ranch Resort project area. The following is a review of this memorandum by Public Utilities. The memorandum uses a simple method to estimate the increased salt and nutrient loading from the project area. The method used is to calculate the rate of runoff from the various parts of the project area and assume a concentration of salt in the runoff. Then a calculation is applied: the runoff rate multiplied by the concentration yields load. While this method can be valid, it is of course dependent on the accuracy of the assumption about the concentration of salt in the runoff from the project area. The memorandum (page 3, first paragraph) states that runoff from developed project areas is assumed to have salt concentration of 800 mg/l. It would be well if the memorandum documented the sources of this information; that is to say, references should be cited. A different approach would be to estimate the amount of salt applied to the ground surface of the developed areas; e.g. pounds of salt applied per acre per year. Salt is applied in the form of landscape water, fertilizers, soil amendments, pet wastes, and other human activities. Because salt is nearly perfectly conservative, one can assume that all the applied salt eventually gets to the reservoir. This approach was not used. It is not clear which approach would be more accurate. A similar discussion holds for estimating the increased loading of nitrogen and phosphorous to the reservoir, with the exception that some nitrogen and some phosphorous is removed by the BMP treatment features of the project. In the memorandum the assumed concentrations of nitrogen and phosphorous in runoff from developed project areas are given on p. 3, last paragraph and in the third table, respectively. No references are cited for these values.

Page 2 Ms. Jeanette Temple February 13, 2012 The assessment presented in the memorandum is that the project will increase salt and nutrient loading to the reservoir by certain amounts. The memorandum provides the following: increased load to

Otay Reservoir, lbs/yr

percentage increase in Otay Reservoir when the reservoir is full; i.e., 49,850 AF

Salt [as TDS] 254,000 0.4% nitrogen 1,400 2.3% phosphorous 58 no percentage increase is stated

The effect of salt or nutrient loading on the reservoir will depend on the volume of water in storage. Lower Otay Reservoir is rarely full. At smaller reservoir volumes the effects will be greater. We recommend describing salt and nutrient loading relative to reservoir volumes that can reasonably be expected over the lifespan of the Otay Ranch Resort project. We suggest using the average reservoir volume and the 30th percentile reservoir volume. Using a thirty year period of record [1980 to 2010] of storage in Lower Otay Reservoir, we have roughly calculated the percentage increase in salt and nitrogen at average storage and 30th percentile storage. increased load to

Otay Reservoir, lbs/yr

Percentage increase in Otay Reservoir at average storage; i.e., 40,300 AF *

Percentage increase in Otay Reservoir at 30th percentile storage; i.e., 37,200 AF *

Salt [as TDS] 254,000 0.5% 0.6% nitrogen 1,400 2.8% 3.1% phosphorous 58 no data available

*These storage volumes are derived from records of hydrographic data archived by the City. These data are available upon request. In summation: We have no reason to disagree with the numerical results presented in the memorandum. References should be cited. The increases in salt and nutrient loading should be described relative to the average reservoir volume and the 30th percentile reservoir volume. The memorandum’s assumptions, calculations, and results should be disclosed in the project’s Environmental Impact Report documents. Jeffery Pasek Watershed Manager cc: Marsi A. Steirer, Deputy Director, Long-Range Planning & Water Resources Division Cecilia Gallardo, Assistant Deputy Director, Development Services Anna McPherson, Senior Planner, Development Services RMU 2.0